1. Field of the Invention
The present invention generally relates to a reference-voltage generating circuit, and especially relates to a reference-voltage generating circuit used for a temperature detector and a thermometer.
2. Description of the Related Art
In recent years and continuing, there is a reference-voltage generating circuit that generates a reference voltage by adding a voltage Vptat that has a positive temperature coefficient, and a voltage Vpn that has a negative temperature coefficient using the principle of the work function difference of gates (for example, Patent Reference 1 refers). Such a reference-voltage generating circuit, using the principle of the work function difference of the gates, adds the voltage Vptat that has a positive temperature coefficient and the voltage Vpn that has a negative temperature coefficient for generating a predetermined reference voltage Vref.
FIG. 10 is a circuit diagram showing an example of a conventional reference-voltage generating circuit.
The reference-voltage generating circuit shown by FIG. 10 includes n channel type field-effect transistors (n-type transistors) M1 through M4 wherein concentrations of substrate impurities and channel dopant are equal, and the n-type transistors are formed in a p-well of an n-type substrate. For each of the n-type transistors M1 through M4, a substrate potential and a source potential are made equal to each other. Further, the n-type transistor M1 has a high concentration n-type gate, and the n-type transistor M2 has a high concentration p-type gate. Further, the ratios S of the channel width W to the channel length L (i.e., S=W/L) of the n-type transistors M1 and M2 are set equal to each other.
Further, the n-type transistor M3 has a high concentration n-type gate, and the n-type transistor M4 has a low concentration n-type gate. Further, the ratios S of the channel width W to the channel length L (i.e., S=W/L) of the n-type transistors M3 and M4 are set equal to each other. The n-type transistor M1 serves as a constant-current power supply, and the same current flows through the n-type transistors M1 and M2. Accordingly, voltages V1 and V2 (refer to FIG. 10) are expressed as follows, where Vpn represents a voltage between the source and the gate of the n-type transistor M2, and R1 and R2 represent the resistance values of resistors R1 and R2, respectively.V1=VpnV2=R2×Vpn/(R1+R2)
Further, since the n-type transistor M4 serves as a constant-current power supply, the same current flows through the n-type transistors M3 and M4, gates of which have different impurity concentrations, and the voltage between the source and the gate of the n-type transistor M3 becomes −Vptat. Given that the voltage V2 is applied to the gate of the n-type transistor M3, the source voltage V3 of the n-type transistor M3 is expressed as follows.
                    V3        =                  V2          -                      (                          -              Vptat                        )                                                  =                              R2            ×                          Vpn              /                              (                                  R1                  +                  R2                                )                                              +                      Vptat            ⁢                                                  ⁢                          (                                                =                                ⁢                Vref                            )                                          
FIG. 11 shows an example of the Vg-Id characteristics of the gate voltage Vg vs. the drain current Id of the n-type transistors M1 through M4. As for the n-type transistor M1, the gate is connected to the source, and a drain current Id1 flows. The same current Id1 flows through the n-type transistor M2 that is connected in series with the n-type transistor M1. Accordingly, the voltage Vpn is equal to the voltage difference between the gate voltage Vg of the n-type transistor M1 and the gate voltage Vg of the n-type transistor M2. Further, as for the n-type transistor M4, wherein the gate is connected to the source, a drain current Id4 flows. Since the n-type transistor M3 is connected in series with the n-type transistor M4, the same current Id4 flows through the transistor M3. Accordingly, the voltage difference between the gate voltage Vg of the n-type transistor M3 and the gate voltage Vg of the n-type transistor M4 is equal to the voltage Vptat. The sum of the voltage Vpn and the voltage Vptat serves as the reference voltage Vref.
On the other hand, voltages Vds1 through Vds4 between the drains and the sources of the n-type transistors M1 through M4, respectively, are expressed as follows, given that the voltage of the point connecting the n-type transistors M1 and M2 is equal to V1+Vgs5, where Vgs5 represents the voltage between the gate and the source of an n-type transistor M5, and the voltage of the point connecting the n-type transistors M3 and M4 is V3.Vds1=Vcc−(V1+Vgs5)=Vcc−(Vpn+Vgs5)Vds2=V1+Vgs5=Vpn+Vgs5Vds3=Vcc−V3=Vcc−VrefVds4=V3=Vref
[Patent Reference 1]
JPA, 2001-284464